Motor vehicles often employ a hitch assembly for towing a trailer. The typical hitch assembly is mounted to the rear of the motor vehicle and includes a hitch receiver or receiver tube and a removable hitch bar. The hitch receiver tube is fixedly mounted to the motor vehicle using brackets and/or welds, and is sized to receive the hitch bar therein. The hitch bar typically has a ball or tongue onto which the trailer is mounted.
In most conventional hitch assemblies, the hitch receiver tube includes a reinforcing collar or ring mounted on the end of the hitch receiver tube into which the hitch bar is inserted. The protective collar or ring protects the inside shape of the tube from being deformed. Typically this protective collar or ring is welded onto the hitch receiver tube. While this method of construction has served well in the past, welding of the collar or ring onto the hitch receiver tube has several disadvantages. For one, the weld, which is visible from the rear of the motor vehicle on which the receiver is installed, is not aesthetically pleasing. Second, the weld increases the likelihood of water and debris such as road salt being retained in the receiver, which can result in the formation of rust and reduce the overall useful life of the receiver. Finally, using a multiple piece assembly for the hitch receiver tube results in greater shipping, handling, and manufacturing costs than does employing a single piece assembly.
An additional problem associated with prior art receivers is that their method of manufacture frequently resulted in voids in the inside wall of the receiver. These voids tend to weaken the strength of the receiver and serve as gathering locations for moisture and other debris such as road salt which, over time, lead to corrosion and tend to shorten the useful life of the receiver.
To overcome the abovementioned problems associated with prior art receivers, including multi-piece receivers, some have developed a method of forming a one-piece trailer receiver tube using hollow forward extrusion, such as disclosed in U.S. Pat. No. 6,931,904 (the “'904 patent”), More specifically, the '904 patent discloses a method of forging a trailer receiver tube by providing a die having an inner surface defining a first portion and a second portion, a hollow tube having an outer surface, and a punch having a body and a shaft extending therefrom sized to fit within the hollow tube. The hollow tube is loaded within the first portion of the die, and the punch is then inserted into the hollow tube such that the body abuts an end of the hollow tube and the shaft extends therethrough. The punch and the hollow tube is then advanced through the die such that a portion of the hollow tube is extruded into the second portion of the die and the outer surface of the hollow tube conforms to the inner surface of the die to thereby form the trailer receiver tube.
However, this method of forging is undesirable for a number of reasons. First, the method of forging a trailer receiver tube described in the '904 patent does not address the customer driven request for a rounded or smooth outer edge on the head portion. Rather, the method taught by the '904 patent results in a receiver with a sharp edge on the head portion which can cause injury to an operator engaging or disengaging the trailer tube assembly, which is both dangerous and undesirable. In an effort to remove said sharp edge, some operators have incorporated post processing techniques such as grinding down the edge, which is both costly and time consuming and therefore inefficient.
Second, prior art devices such as the one used in the '904 patent tend to fail prematurely. It is believed that this premature failure is due in part to excess pressure buildup in the cavity of the device Once the device fails, the operator must either repair or replace the failed device, which can be both costly and time consuming and therefore inefficient.
So that the structure, method, operation and advantages of the trailer receiver of the present invention can be best understood, a prior art method of forming a trailer receiver tube using cold forward extrusion is described below and shown in FIGS. 1 through 4. Referring to FIG. 1 of the drawings, there is illustrated receiver tube 10 formed in accordance with the method described in the '904 patent. Receiver tube 10 is intended to be mounted beneath the floor pan or bumper of a motor vehicle (not shown), and is configured to receive a conventional hitch bar (not shown) of a type that is well known in the art. Receiver tube 10 is unitarily formed and has a generally rectangular lateral cross section and comprises outer surface 11, head portion 12 and body portion 14. As illustrated in FIG. 1, head portion 12 transitions to body portion 14 through chamfered portion 16.
Head portion 12 is located at a distal end of receiver tube 10 for receipt of a hitch bar (not shown) and provides a protective collar around receiver tube 10. Body portion 14 extends from head portion 12 in the direction of the motor vehicle (not shown) and is adapted for mounting on said vehicle. Body portion 14 further comprises hole 18 formed therein for receiving a locking pin (not shown) once the hitch bar (not shown) has been inserted into receiver tube 10.
As illustrated in FIGS. 2 and 3, receiver tube 10 is formed using hollow forward (direct) extrusion. Die 19 is provided that defines inner surface 24 having first portion 26 and second portion 28. First portion 26 is characterized as defining an opening that is somewhat larger than that of second portion 28. Chamfer forming portion 30 extends between first portion 26 and second portion 28, and is used to form chamfered portion 16 as described more fully below.
Tubular blank 32 is provided, which is made from a unitary piece of material, such as an ATSM A500 grade steel, or some other suitable material. Tubular blank 32 is illustrated to have a rectangular cross-sectional area, but those skilled in the art will appreciate that various other shaped cross sections may be employed. During the loading stage, as depicted in FIG. 2, tubular blank 32 is placed in die 19 within first portion 26. Tubular blank 32 is sized relatively larger than second portion 28 of die 19 and, as such, remains within first portion 26 during the loading stage.
Punch 40 is provided having body 42, shaft 44 that extends from an end of body 42 and base 46 that is formed on an opposite end of body 42. Contact surface 48 is formed at the transition between body 42 and shaft 44, and body 42 is sized to fit within first portion 26 of die 19. Shaft 44 is sized to fit within tubular blank 32.
During the loading stage as shown in FIG. 2, punch 40 is inserted into tubular blank 32 such that shaft 44 extends into tubular blank 32 and contact surface 48 engages loading end 36. As illustrated in FIG. 2, shaft 44 extends completely through tubular blank 32 at this stage.
Receiver tube 10 is formed by hollow forward extruding blank 32 through die 19 using the punch 40 as illustrated in FIG. 3. Preferably, punch 40 is urged into die 19 under ambient temperature conditions by a press ram (not shown). Alternatively, punch 40 may be urged into die 19 at elevated temperatures. The contact surface 48 engages tubular blank 32 and forces tubular blank 32 into second portion 28 of die 19.
Fixed between shaft 44 of punch 40 and die 19, tubular blank 32 is subjected to compression forces as it is urged into second portion 28 causing tubular blank 32 to increase in longitudinal length while simultaneously decreasing in wall thickness. The portion of tubular blank 32 that is extruded into second portion 28 forms body portion 14 of receiver tube 10.
Punch 40 is urged into die 19 by a press ram (not shown) until such time as shim blocks (not shown) or a stroke limit on the press ram terminates the movement of punch 40. A portion of tubular blank 32 remains within first portion 26 of die 19 (i.e. is not extruded through second portion 28) and thus forms head portion 12. Accordingly, head portion 12 retains the characteristics of blank 32 prior to insertion into die 19, and acts as a reinforcing area for newly formed receiver tube 10. Chamfer forming portion 30 forms chamfered portion 16 which acts as the transition between head portion 12 and body portion 14. Punch 40 is then retracted from die 19 by a reverse stroke of the press ram (not shown). At that time, a knock-out stroke is initiated by the press ram to remove receiver tube 10 from die 19. Using the above extrusion method, outer surface 11 of receiver tube 10 is defined by inner surface 24 of die 19.
Turning now to FIG. 4 which depicts the cross-sectional view of head portion 12, chamfered portion 16, and body portion 14 of receiver tube 10 and illustrates the alignment of the grain within receiver tube 10 after forming using the method described above. Specifically, the grain of the material within head portion 12 and body portion 14 extends parallel to the longitudinal axis of receiver tube 10 (e.g. in the direction of the cold forward extrusion), and the grain in chamfered portion 16 runs at an angle to the longitudinal axis of receiver tube 10 and parallel to the outer surface of chamfered portion 16. The grains within body portion 14 are also compressed and closer together than the grains within head portion 12. By preserving the grain flow of tubular blank 32 within head portion 12, characteristics such as grain ends or voids are eliminated, and using cold forward extrusion to form body portion 14 preserves directional grain alignment.
Notwithstanding, the forgoing, the method of forming a trailer receiver tube described in the '904 patent results in a receiver with a number of undesirable characteristics. More specifically, the method described in the '904 patent does not address the customer driven request for a rounded or smooth outer edge on the head portion thereby necessitating secondary processing techniques such as grinding, which is both time consuming and costly, to avoid potential injury to the receiver operator due to the sharp surface. The method also does not address the customer driven demand for an angle between head portion 12 and chamfered portion 16 that is in excess of 30 degrees.